Measuring the responses of organs in a body is becoming more common with the development of small implantable biological sensors. For example, the continuous measurement of blood flow in vessels, particularly in postoperative cases, is desirable for the evaluation of vascular reconstructive operations, organ transplants and other medical procedures. Various blood flow velocity (and diameter) sensors have been developed including electromagnetic type flow meters and pulsed ultrasonic Doppler transducers consisting of a single piezoelectric crystal acting as an ultrasonic transmitter and receiver. The flow velocity sensors, particularly the Doppler flow probe, are very small and can be used inside a patient.
The small flow probes can be used to monitor continuously blood flow in a patient for a period of time, postoperative or otherwise. The sensor or probe must be secured to the vessel to assure proper flow velocity measurements. There is a great advantage of being able to remove the probe after implantation during surgery without resorting to additional surgical procedure.
The objective of a removable flow probe which gives reliable monitoring data of a vessel has been sought by suturing, embedding or attaching the probe directly to the vessel or associated outer tissue. The removal of the probe involved pulling lead wires or other lines from the probe to pull out the probe attachment. This can damage tissue including the grafted vessel or vessel which was monitored.
For example probes have been sutured to be adventitia, the layer of tissue on the outside of a vessel, and removed by pulling on the suture and probe. Payen, D. et al, "Comparison of Preoperative and Postoperative Phasic Blood Flow in Aortocoronary Venous Bypass Grafts by Means of Pulsed Doppler Echocardiography with Implantable Microprobes," Circ; Vol. 74. (Suppl. III), pp. 61-67 (1986); Svenning, J. L. et al, "Continuous Monitoring of Cardiac Output Postoperatively Using an Implantable Doppler Probe," Scand. J. Thor. Cardiovasc. Surg., Vol. 20, pp. 145-149 (1986). Another example, shown in Baudino, U.S. Pat. No. 4,541,433 issued Sept. 17, 1985, is a Doppler sensor with small metal tines in the tip of the probe. The tines are embedded in the adventitia. The device is removed by pulling on the probe so the tines are withdrawn from the adventitia.
The extractable, implantable probes of prior inventions must be attached loosely so that removal can be achieved. A loose attachment causes the potential for positional instability. The alignment of the probe must be stable in order to properly measure the flow through the vessel. Also, suturing and puncturing techniques used with probe attachment are potentially traumatic to the vessel. Suturing is potentially traumatic especially to a small vessel.